Several processes for the modification of (co)polymers with peroxides are known from the prior art. In many of these processes, unsaturated peroxides are employed. Some examples of these processes can be found in EP-A-0322945 and WO 94/05707.
In addition, Canadian Patent 999,698 teaches that methylethyl ketone peroxides can be used to reduce the viscosity of a-olefinic polymers. Further, EP-A-0-497590 and EP-A-0264156 are examples of patents which suggest the use of methylethyl ketone peroxide and methylisobutyl ketone peroxide for increasing the melt flow index of polypropylene.
Methylethyl ketone peroxide and methylisobutyl ketone peroxide are known to be mixtures of several different ketone peroxide compounds, among which the noncyclic ketone peroxides predominate. However, these ketone peroxides do contain some small quantities of cyclic ketone peroxides which result from side reactions during the preparation of the methylethyl and methylisobutyl ketone peroxides. For example, in commercially available methylethyl ketone peroxides about 1-4% of the total active oxygen content is attributable to cyclic ketone peroxides.
Although these peroxides are known for use in the modification of polymers, their performance in, for example, polypropylene degradation is disappointing and they often cause yellowing of the polymer. Thus, while these peroxides increase the melt flow index of polypropylene, they are not nearly as effective as commercial products such as 2,5-bis(tertiarybutylperoxy)-2,5-dimethyl hexane in this application. The present peroxides offer a performance which is comparable to that of the commercially available peroxides and offer the further advantage that less undesirable by-products are generated by side reactions of the peroxides during their decomposition.
Accordingly, there remains a need in the art for peroxides which provide an acceptable price/performance ratio in polymer modification. These and other objects of the present invention will be apparent from the summary and detailed description of the present invention which follow.